Method and apparatus to perform asynchronous shifts with oncoming slipping clutch torque for a hybrid powertrain system

ABSTRACT

A method to control a powertrain including a transmission, an engine, and an electric machine includes monitoring a desired transmission shift including an oncoming clutch, monitoring operational parameters of the powertrain, monitoring a maximum electric machine torque capacity, determining a desired output torque profile through the desired transmission shift, determining a maximum electric machine torque capability profile through the desired transmission shift based upon the maximum electric machine torque capacity and the operational parameters, comparing the desired output torque profile to the maximum electric machine torque capability profile, determining a preferred oncoming clutch torque profile through the desired transmission shift based upon the comparing, and executing a clutch assisted shift based upon the preferred oncoming clutch torque profile.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/985,283 filed on Nov. 4, 2007 which is hereby incorporated herein byreference.

TECHNICAL FIELD

This disclosure pertains to control systems for electro-mechanicaltransmissions.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Known powertrain architectures include torque-generative devices,including internal combustion engines and electric machines, whichtransmit torque through a transmission device to an output member. Oneexemplary powertrain includes a two-mode, compound-split,electro-mechanical transmission which utilizes an input member forreceiving motive torque from a prime mover power source, preferably aninternal combustion engine, and an output member. The output member canbe operatively connected to a driveline for a motor vehicle fortransmitting tractive torque thereto. Electric machines, operative asmotors or generators, generate an input torque to the transmission,independently of an input torque from the internal combustion engine.The electric machines may transform vehicle kinetic energy, transmittedthrough the vehicle driveline, to electrical energy that is storable inan electrical energy storage device. A control system monitors variousinputs from the vehicle and the operator and provides operationalcontrol of the powertrain, including controlling transmission operatingrange state and gear shifting, controlling the torque-generativedevices, and regulating the electrical power interchange among theelectrical energy storage device and the electric machines to manageoutputs of the transmission, including torque and rotational speed.

Transmissions within a hybrid powertrain, as described above, serve anumber of functions by transmitting and manipulating torque in order toprovide torque to an output member. In order to serve the particularfunction required, the transmission selects between a number ofoperating range states or configurations internal to the transmissiondefining the transfer of torque through the transmission. Knowntransmissions utilize operating range states including fixed gear statesor states with a defined gear ratio. For example, a transmission canutilize four sequentially arranged fixed gear states and allow selectionbetween the four gear states in order to provide output torque through awide range of output member speeds. Additively or alternatively, knowntransmissions also allow for continuously variable operating rangestates or mode states, enabled for instance through the use of aplanetary gear set, wherein the gear ratio provided by the transmissioncan be varied across a range in order to modulate the output speed andoutput torque provided by a particular set of inputs. Additionally,transmissions can operate in a neutral state, ceasing all torque frombeing transmitted through the transmission. Additionally, transmissionscan operate in a reverse mode, accepting input torque in a particularrotational direction used for normal forward operation and reversing thedirection of rotation of the output member. Through selection ofdifferent operating range states, transmissions can provide a range ofoutputs for a given input.

Operation of the above devices within a hybrid powertrain vehiclerequire management of numerous torque bearing shafts or devicesrepresenting connections to the above mentioned engine, electricalmachines, and driveline. Input torque from the engine and input torquefrom the electric machine or electric machines can be appliedindividually or cooperatively to provide output torque. However, changesin output torque required from the transmission, for instance, due to achange in operator pedal position or due to an operating range stateshift, must be handled smoothly. Particularly difficult to manage areinput torques, applied simultaneously to a transmission, with differentreaction times to a control input. Based upon a single control input,the various devices can change respective input torques at differenttimes, causing increased abrupt changes to the overall torque appliedthrough the transmission. Abrupt or uncoordinated changes to the variousinput torques applied to a transmission can cause a perceptible changein acceleration or jerk in the vehicle, which can adversely affectvehicle drivability.

Various control schemes and operational connections between the variousaforementioned components of the hybrid drive system are known, and thecontrol system must be able to engage to and disengage the variouscomponents from the transmission in order to perform the functions ofthe hybrid powertrain system. Engagement and disengagement are known tobe accomplished within the transmission by employing selectivelyoperable clutches. Clutches are devices well known in the art forengaging and disengaging shafts including the management of rotationalvelocity and torque differences between the shafts. Engagement orlocking, disengagement or unlocking, operation while engaged or lockedoperation, and operation while disengaged or unlocked operation are allclutch states that must be managed in order for the vehicle to operateproperly and smoothly.

Clutches are known in a variety of designs and control methods. Oneknown type of clutch is a mechanical clutch operating by separating orjoining two connective surfaces, for instance, clutch plates, operating,when joined, to apply frictional torque to each other. One controlmethod for operating such a mechanical clutch includes applying ahydraulic control system implementing fluidic pressures transmittedthrough hydraulic lines to exert or release clamping force between thetwo connective surfaces. Operated thusly, the clutch is not operated ina binary manner, but rather is capable of a range of engagement states,from fully disengaged, to synchronized but not engaged, to engaged butwith only minimal clamping force, to engaged with some maximum clampingforce. Clamping force applied to the clutch determines how much reactivetorque the clutch can carry before the clutch slips. Variable control ofclutches through modulation of clamping force allows for transitionbetween locked and unlocked states and further allows for managing slipin a locked transmission. In addition, the maximum clamping forcecapable of being applied by the hydraulic lines can also vary withvehicle operating states and can be modulated based upon controlstrategies.

Clutches are known to be operated asynchronously, designed toaccommodate some level of slip in transitions between locked andunlocked states. Other clutches are known to be operated synchronously,designed to match speeds of connective surfaces or synchronize beforethe connective surfaces are clamped together. This disclosure dealsprimarily with clutches designed for primarily synchronous operation.

Slip, or relative rotational movement between the connective surfaces ofthe clutch when the clutch connective surfaces are intended to besynchronized and locked, occurs whenever reactive torque applied to theclutch exceeds actual torque capacity created by applied clamping force.Slip in a transmission utilizing clutches designed for synchronousoperation results in unintended loss of torque control within thetransmission, results in loss of engine speed control and electricmachine speed control caused by a sudden change in back-torque from thetransmission, and results in sudden changes to vehicle acceleration,creating adverse affects to drivability.

Transmissions can operate with a single clutch transmitting reactivetorque between inputs and an output. Transmission can operate with aplurality of clutches transmitting reactive torque between inputs and anoutput. Selection of operating range state depends upon the selectiveengagement of clutches, with different allowable combinations resultingin different operating range states.

Transition from one operating state range to another operating staterange involves transitioning at least one clutch state. An exemplarytransition from one fixed gear state to another involves unloading afirst clutch, transitioning through a freewheeling, wherein no clutchesremain engaged, or inertia speed phase state, wherein at least oneclutch remains engaged, and subsequently loading a second clutch. Adriveline connected to a locked and synchronized clutch, prior to beingunloaded, is acted upon by an output torque resulting through thetransmission as a result of input torques and reduction factors presentin the transmission. In such a torque transmitting state, thetransmission so configured during a shift is said to be in a torquephase. In a torque phase, vehicle speed and vehicle acceleration arefunctions of the output torque and other forces acting upon the vehicle.Unloading a clutch removes all input torque from a previously locked andsynchronized clutch. As a result, any propelling force previouslyapplied to the output torque through that clutch is quickly reduced tozero. In one exemplary configuration, another clutch remains engaged andtransmitting torque to the output while the transmission synchronizesthe second clutch. In such a configuration, the transmission is in aninertia speed phase. As the second clutch to be loaded is synchronizedand loaded, the transmission again enters a torque phase, whereinvehicle speed and vehicle acceleration are functions of the outputtorque and other forces acting upon the vehicle. While output torquechanges or interruptions due to clutch unloading and loading are anormal part of transmission operating range state shifts, orderlymanagement of the output torque changes reduces the impact of the shiftsto drivability.

As described above, slip in a clutch designed for synchronous operationis frequently an undesirable result. However, particular clutch designsmay still allow controlled slip within an otherwise synchronous controlscheme top achieve particular goals. An exemplary goal in whichcontrolled slip could be useful is in assisting control of an inputmember to the clutch to a new input speed. A method to utilize asynchronous clutch through a controlled slip event to assist in controlof an input member would be beneficial to aspects of clutch operation.

SUMMARY

A powertrain includes an electro-mechanical transmissionmechanically-operatively coupled to an internal combustion engine and anelectric machine adapted to selectively transmit mechanical power to anoutput member. A method to control the powertrain includes monitoring adesired transmission shift including an oncoming clutch, monitoringoperational parameters of the powertrain, monitoring a maximum electricmachine torque capacity, determining a desired output torque profilethrough the desired transmission shift, determining a maximum electricmachine torque capability profile through the desired transmission shiftbased upon the maximum electric machine torque capacity and theoperational parameters, comparing the desired output torque profile tothe maximum electric machine torque capability profile, determining apreferred oncoming clutch torque profile through the desiredtransmission shift based upon the comparing, and executing a clutchassisted shift based upon the preferred oncoming clutch torque profile.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of an exemplary powertrain comprising atwo-mode, compound-split, electro-mechanical hybrid transmissionoperatively connected to an engine and first and second electricmachines, in accordance with the present disclosure;

FIG. 2 is a schematic block diagram of an exemplary distributed controlmodule system, in accordance with the present disclosure;

FIG. 3 graphically depicts reaction times of exemplary hybrid powertraincomponents to changes in torque request, in accordance with the presentdisclosure;

FIG. 4 demonstrates gear transition relationships for an exemplaryhybrid powertrain transmission, in particular as described in theexemplary embodiment of FIG. 1 and Table 1, in accordance with thepresent disclosure;

FIGS. 5-7 depict exemplary processes combining to accomplish anexemplary transmission shift, in accordance with the present disclosure;

FIG. 5 is a graphical representation of torque terms associated with aclutch through an exemplary transitional unlocking state;

FIG. 6 is a graphical representation of torque terms associated with aclutch through an exemplary transitional locking state;

FIG. 7 is a graphical representation of terms describing an exemplaryinertia speed phase of a transmission, in accordance with the presentdisclosure;

FIG. 8 illustrates in tabular form use of an exemplary 2D look-up tableto determine inertia speed phase times, in accordance with the presentdisclosure;

FIG. 9 describes an exemplary inertia speed phase divided into threesub-phases, in accordance with the present disclosure;

FIG. 10 is a graphical representation of an instance where a systemicrestraint is imposed upon an immediate control signal, temporarilyoverriding max\min values set by the control signal, in accordance withthe present disclosure;

FIGS. 11 and 12 graphically contrast an exemplary synchronous shift andan asynchronous shift utilized to provide T_(C) through the shift, inaccordance with the present disclosure;

FIG. 11 is an exemplary synchronous shift, as described in the exemplaryembodiments disclosed herein, in accordance with the present disclosure;

FIG. 12 is an exemplary asynchronous shift to provide T_(C) through theshift in order to assist changes to N_(I), in accordance with thepresent disclosure;

FIG. 13 graphically illustrates exemplary use of output torque termsdescribed herein through a transmission shift, in accordance with thepresent disclosure;

FIG. 14 graphically illustrates exemplary use of input and output torqueterms including limiting terms through a transmission shift, inaccordance with the present disclosure;

FIG. 15 illustrates an exemplary process by which a powertrain incontrolled through an inertia speed phase, utilizing oncoming clutchtorque to maintain an output torque, in accordance with the presentdisclosure;

FIG. 16 shows an exemplary control system architecture for controllingand managing torque and power flow in a powertrain system havingmultiple torque generative devices and residing in control modules inthe form of executable algorithms and calibrations, in accordance withthe present disclosure; and

FIG. 17 is a schematic diagram exemplifying data flow through a shiftexecution, describing more detail exemplary execution of the controlsystem architecture of FIG. 16 in greater detail, in accordance with thepresent disclosure.

DETAILED DESCRIPTION

Referring now to the drawings, wherein the showings are for the purposeof illustrating certain exemplary embodiments only and not for thepurpose of limiting the same, FIGS. 1 and 2 depict an exemplaryelectro-mechanical hybrid powertrain. The exemplary electro-mechanicalhybrid powertrain in accordance with the present disclosure is depictedin FIG. 1, comprising a two-mode, compound-split, electro-mechanicalhybrid transmission 10 operatively connected to an engine 14 and firstand second electric machines (‘MG-A’) 56 and (‘MG-B’) 72. The engine 14and first and second electric machines 56 and 72 each generate powerwhich can be transmitted to the transmission 10. The power generated bythe engine 14 and the first and second electric machines 56 and 72 andtransmitted to the transmission 10 is described in terms of inputtorques, referred to herein as T_(I), T_(A), and T_(B) respectively, andspeed, referred to herein as N_(I), N_(A), and N_(B), respectively.

The exemplary engine 14 comprises a multi-cylinder internal combustionengine selectively operative in several states to transmit torque to thetransmission 10 via an input shaft 12, and can be either aspark-ignition or a compression-ignition engine. The engine 14 includesa crankshaft (not shown) operatively coupled to the input shaft 12 ofthe transmission 10. A rotational speed sensor 11 monitors rotationalspeed of the input shaft 12. Power output from the engine 14, comprisingrotational speed and output torque, can differ from the input speed,N_(I), and the input torque, T_(I), to the transmission 10 due toplacement of torque-consuming components on the input shaft 12 betweenthe engine 14 and the transmission 10, e.g., a hydraulic pump (notshown) and/or a torque management device (not shown).

The exemplary transmission 10 comprises three planetary-gear sets 24, 26and 28, and four selectively engageable torque-transmitting devices,i.e., clutches C1 70, C2 62, C3 73, and C4 75. As used herein, clutchesrefer to any type of friction torque transfer device including single orcompound plate clutches or packs, band clutches, and brakes, forexample. A hydraulic control circuit 42, preferably controlled by atransmission control module (hereafter ‘TCM’) 17, is operative tocontrol clutch states. Clutches C2 62 and C4 75 preferably comprisehydraulically-applied rotating friction clutches. Clutches C1 70 and C373 preferably comprise hydraulically-controlled stationary devices thatcan be selectively grounded to a transmission case 68. Each of theclutches C1 70, C2 62, C3 73, and C4 75 is preferably hydraulicallyapplied, selectively receiving pressurized hydraulic fluid via thehydraulic control circuit 42.

The first and second electric machines 56 and 72 preferably comprisethree-phase AC machines, each including a stator (not shown) and a rotor(not shown), and respective resolvers 80 and 82. The motor stator foreach machine is grounded to an outer portion of the transmission case68, and includes a stator core with coiled electrical windings extendingtherefrom. The rotor for the first electric machine 56 is supported on ahub plate gear that is operatively attached to shaft 60 via the secondplanetary gear set 26. The rotor for the second electric machine 72 isfixedly attached to a sleeve shaft hub 66.

Each of the resolvers 80 and 82 preferably comprises a variablereluctance device including a resolver stator (not shown) and a resolverrotor (not shown). The resolvers 80 and 82 are appropriately positionedand assembled on respective ones of the first and second electricmachines 56 and 72. Stators of respective ones of the resolvers 80 and82 are operatively connected to one of the stators for the first andsecond electric machines 56 and 72. The resolver rotors are operativelyconnected to the rotor for the corresponding first and second electricmachines 56 and 72. Each of the resolvers 80 and 82 is signally andoperatively connected to a transmission power inverter control module(hereafter ‘TPIM’) 19, and each senses and monitors rotational positionof the resolver rotor relative to the resolver stator, thus monitoringrotational position of respective ones of first and second electricmachines 56 and 72. Additionally, the signals output from the resolvers80 and 82 are interpreted to provide the rotational speeds for first andsecond electric machines 56 and 72, i.e., N_(A) and N_(B), respectively.

The transmission 10 includes an output member 64, e.g. a shaft, which isoperably connected to a driveline 90 for a vehicle (not shown), toprovide output power, e.g., to vehicle wheels 93, one of which is shownin FIG. 1. The output power is characterized in terms of an outputrotational speed, N_(O) and an output torque, T_(O). A transmissionoutput speed sensor 84 monitors rotational speed and rotationaldirection of the output member 64. Each of the vehicle wheels 93, ispreferably equipped with a sensor 94 adapted to monitor wheel speed,V_(SS-WHL), the output of which is monitored by a control module of adistributed control module system described with respect to FIG. 2, todetermine vehicle speed, and absolute and relative wheel speeds forbraking control, traction control, and vehicle acceleration management.

The input torques from the engine 14 and the first and second electricmachines 56 and 72 (T_(I), T_(A), and T_(B) respectively) are generatedas a result of energy conversion from fuel or electrical potentialstored in an electrical energy storage device (hereafter ‘ESD’) 74. TheESD 74 is high voltage DC-coupled to the TPIM 19 via DC transferconductors 27. The transfer conductors 27 include a contactor switch 38.When the contactor switch 38 is closed, under normal operation, electriccurrent can flow between the ESD 74 and the TPIM 19. When the contactorswitch 38 is opened electric current flow between the ESD 74 and theTPIM 19 is interrupted. The TPIM 19 transmits electrical power to andfrom the first electric machine 56 by transfer conductors 29, and theTPIM 19 similarly transmits electrical power to and from the secondelectric machine 72 by transfer conductors 31, in response to torquerequests to the first and second electric machines 56 and 72 to achievethe input torques T_(A) and T_(B). Electrical current is transmitted toand from the ESD 74 in accordance with whether the ESD 74 is beingcharged or discharged.

The TPIM 19 includes the pair of power inverters (not shown) andrespective motor control modules (not shown) configured to receive thetorque commands and control inverter states therefrom for providingmotor drive or regeneration functionality to meet the commanded motortorques T_(A) and T_(B). The power inverters comprise knowncomplementary three-phase power electronics devices, and each includes aplurality of insulated gate bipolar transistors (not shown) forconverting DC power from the ESD 74 to AC power for powering respectiveones of the first and second electric machines 56 and 72, by switchingat high frequencies. The insulated gate bipolar transistors form aswitch mode power supply configured to receive control commands. Thereis typically one pair of insulated gate bipolar transistors for eachphase of each of the three-phase electric machines. States of theinsulated gate bipolar transistors are controlled to provide motor drivemechanical power generation or electric power regenerationfunctionality. The three-phase inverters receive or supply DC electricpower via DC transfer conductors 27 and transform it to or fromthree-phase AC power, which is conducted to or from the first and secondelectric machines 56 and 72 for operation as motors or generators viatransfer conductors 29 and 31 respectively.

FIG. 2 is a schematic block diagram of the distributed control modulesystem. The elements described hereinafter comprise a subset of anoverall vehicle control architecture, and provide coordinated systemcontrol of the exemplary powertrain described in FIG. 1. The distributedcontrol module system synthesizes pertinent information and inputs, andexecutes algorithms to control various actuators to achieve controlobjectives, including objectives related to fuel economy, emissions,performance, drivability, and protection of hardware, includingbatteries of ESD 74 and the first and second electric machines 56 and72. The distributed control module system includes an engine controlmodule (hereafter ‘ECM’) 23, the TCM 17, a battery pack control module(hereafter ‘BPCM’) 21, and the TPIM 19. A hybrid control module(hereafter ‘HCP’) 5 provides supervisory control and coordination of theECM 23, the TCM 17, the BPCM 21, and the TPIM 19. A user interface(‘UI’) 13 is operatively connected to a plurality of devices throughwhich a vehicle operator controls or directs operation of theelectro-mechanical hybrid powertrain. The devices include an acceleratorpedal 113 (‘AP’) from which an operator torque request is determined, anoperator brake pedal 112 (‘BP’), a transmission gear selector 114(‘PRNDL’), and a vehicle speed cruise control (not shown). Thetransmission gear selector 114 may have a discrete number ofoperator-selectable positions, including the rotational direction of theoutput member 64 to enable one of a forward and a reverse direction.

The aforementioned control modules communicate with other controlmodules, sensors, and actuators via a local area network (hereafter‘LAN’) bus 6. The LAN bus 6 allows for structured communication ofstates of operating parameters and actuator command signals between thevarious control modules. The specific communication protocol utilized isapplication-specific. The LAN bus 6 and appropriate protocols providefor robust messaging and multi-control module interfacing between theaforementioned control modules, and other control modules providingfunctionality such as antilock braking, traction control, and vehiclestability. Multiple communications buses may be used to improvecommunications speed and provide some level of signal redundancy andintegrity. Communication between individual control modules can also beeffected using a direct link, e.g., a serial peripheral interface(‘SPI’) bus (not shown).

The HCP 5 provides supervisory control of the powertrain, serving tocoordinate operation of the ECM 23, TCM 17, TPIM 19, and BPCM 21. Basedupon various input signals from the user interface 13 and thepowertrain, including the ESD 74, the HCP 5 generates various commands,including: the operator torque request (‘T_(O) _(—) _(REQ)’), acommanded output torque (‘T_(CMD)’) to the driveline 90, an engine inputtorque request, clutch torques for the torque-transfer clutches C1 70,C2 62, C3 73, C4 75 of the transmission 10; and the torque requests forthe first and second electric machines 56 and 72, respectively. The TCM17 is operatively connected to the hydraulic control circuit 42 andprovides various functions including monitoring various pressure sensingdevices (not shown) and generating and communicating control signals tovarious solenoids (not shown) thereby controlling pressure switches andcontrol valves contained within the hydraulic control circuit 42.

The ECM 23 is operatively connected to the engine 14, and functions toacquire data from sensors and control actuators of the engine 14 over aplurality of discrete lines, shown for simplicity as an aggregatebi-directional interface cable 35. The ECM 23 receives the engine inputtorque request from the HCP 5. The ECM 23 determines the actual engineinput torque, T_(I), provided to the transmission 10 at that point intime based upon monitored engine speed and load, which is communicatedto the HCP 5. The ECM 23 monitors input from the rotational speed sensor11 to determine the engine input speed to the input shaft 12, whichtranslates to the transmission input speed, N_(I). The ECM 23 monitorsinputs from sensors (not shown) to determine states of other engineoperating parameters including, e.g., a manifold pressure, enginecoolant temperature, ambient air temperature, and ambient pressure. Theengine load can be determined, for example, from the manifold pressure,or alternatively, from monitoring operator input to the acceleratorpedal 113. The ECM 23 generates and communicates command signals tocontrol engine actuators, including, e.g., fuel injectors, ignitionmodules, and throttle control modules, none of which are shown.

The TCM 17 is operatively connected to the transmission 10 and monitorsinputs from sensors (not shown) to determine states of transmissionoperating parameters. The TCM 17 generates and communicates commandsignals to control the transmission 10, including controlling thehydraulic control circuit 42. Inputs from the TCM 17 to the HCP 5include estimated clutch torques for each of the clutches, i.e., C1 70,C2 62, C3 73, and C4 75, and rotational output speed, N_(O), of theoutput member 64. Other actuators and sensors may be used to provideadditional information from the TCM 17 to the HCP 5 for controlpurposes. The TCM 17 monitors inputs from pressure switches (not shown)and selectively actuates pressure control solenoids (not shown) andshift solenoids (not shown) of the hydraulic control circuit 42 toselectively actuate the various clutches C1 70, C2 62, C3 73, and C4 75to achieve various transmission operating range states, as describedhereinbelow.

The BPCM 21 is signally connected to sensors (not shown) to monitor theESD 74, including states of electrical current and voltage parameters,to provide information indicative of parametric states of the batteriesof the ESD 74 to the HCP 5. The parametric states of the batteriespreferably include battery state-of-charge, battery voltage, batterytemperature, and available battery power, referred to as a range P_(BAT)_(—) _(MIN) to P_(BAT) _(—) _(MAX).

Each of the control modules ECM 23, TCM 17, TPIM 19 and BPCM 21 ispreferably a general-purpose digital computer comprising amicroprocessor or central processing unit, storage mediums comprisingread only memory (‘ROM’), random access memory (‘RAM’), electricallyprogrammable read only memory (‘EPROM’), a high speed clock, analog todigital (‘A/D’) and digital to analog (‘D/A’) circuitry, andinput/output circuitry and devices (‘I/O’) and appropriate signalconditioning and buffer circuitry. Each of the control modules has a setof control algorithms, comprising resident program instructions andcalibrations stored in one of the storage mediums and executed toprovide the respective functions of each computer. Information transferbetween the control modules is preferably accomplished using the LAN bus6 and SPI buses. The control algorithms are executed during preset loopcycles such that each algorithm is executed at least once each loopcycle. Algorithms stored in the non-volatile memory devices are executedby one of the central processing units to monitor inputs from thesensing devices and execute control and diagnostic routines to controloperation of the actuators, using preset calibrations. Loop cycles areexecuted at regular intervals, for example each 3.125, 6.25, 12.5, 25and 100 milliseconds during ongoing operation of the powertrain.Alternatively, algorithms may be executed in response to the occurrenceof an event.

The exemplary powertrain selectively operates in one of severaloperating range states that can be described in terms of an engine statecomprising one of an engine on state (‘ON’) and an engine off state(‘OFF’), and a transmission state comprising a plurality of fixed gearsand continuously variable operating modes, described with reference toTable 1, below.

TABLE 1 Engine Transmission Operating Applied Description State RangeState Clutches MI_Eng_Off OFF EVT Mode I C1 70 MI_Eng_On ON EVT Mode IC1 70 FG1 ON Fixed Gear Ratio 1 C1 70 C4 75 FG2 ON Fixed Gear Ratio 2 C170 C2 62 MII_Eng_Off OFF EVT Mode II C2 62 MII_Eng_On ON EVT Mode II C262 FG3 ON Fixed Gear Ratio 3 C2 62 C4 75 FG4 ON Fixed Gear Ratio 4 C2 62C3 73

Each of the transmission operating range states is described in thetable and indicates which of the specific clutches C1 70, C2 62, C3 73,and C4 75 are applied for each of the operating range states. A firstcontinuously variable mode, i.e., EVT Mode I, or MI, is selected byapplying clutch C1 70 only in order to “ground” the outer gear member ofthe third planetary gear set 28. The engine state can be one of ON(‘MI_Eng_On’) or OFF (‘MI_Eng_Off’). A second continuously variablemode, i.e., EVT Mode II, or MII, is selected by applying clutch C2 62only to connect the shaft 60 to the carrier of the third planetary gearset 28. The engine state can be one of ON (‘MII_Eng_On’) or OFF(‘MII_Eng_Off’). For purposes of this description, when the engine stateis OFF, the engine input speed is equal to zero revolutions per minute(‘RPM’), i.e., the engine crankshaft is not rotating. A fixed gearoperation provides a fixed ratio operation of input-to-output speed ofthe transmission 10, i.e., N_(I)/N_(O), is achieved. A first fixed gearoperation (‘FG1’) is selected by applying clutches C1 70 and C4 75. Asecond fixed gear operation (‘FG2’) is selected by applying clutches C170 and C2 62. A third fixed gear operation (‘FG3’) is selected byapplying clutches C2 62 and C4 75. A fourth fixed gear operation (‘FG4’)is selected by applying clutches C2 62 and C3 73. The fixed ratiooperation of input-to-output speed increases with increased fixed gearoperation due to decreased gear ratios in the planetary gears 24, 26,and 28. The rotational speeds of the first and second electric machines56 and 72, N_(A) and N_(B) respectively, are dependent on internalrotation of the mechanism as defined by the clutching and areproportional to the input speed measured at the input shaft 12.

In response to operator input via the accelerator pedal 113 and brakepedal 112 as captured by the user interface 13, the HCP 5 and one ormore of the other control modules determine the commanded output torque,T_(CMD), intended to meet the operator torque request, T_(O) _(—)_(REQ), to be executed at the output member 64 and transmitted to thedriveline 90. Final vehicle acceleration is affected by other factorsincluding, e.g., road load, road grade, and vehicle mass. The operatingrange state is determined for the transmission 10 based upon a varietyof operating characteristics of the powertrain. This includes theoperator torque request, communicated through the accelerator pedal 113and brake pedal 112 to the user interface 13 as previously described.The operating range state may be predicated on a powertrain torquedemand caused by a command to operate the first and second electricmachines 56 and 72 in an electrical energy generating mode or in atorque generating mode. The operating range state can be determined byan optimization algorithm or routine, initiated for example within ahybrid strategic control module of the HCP 5, which determines optimumsystem efficiency based upon operator demand for power, battery state ofcharge, and energy efficiencies of the engine 14 and the first andsecond electric machines 56 and 72. The control system manages torqueinputs from the engine 14 and the first and second electric machines 56and 72 based upon an outcome of the executed optimization routine, andsystem efficiencies are optimized thereby, to manage fuel economy andbattery charging. Furthermore, operation can be determined based upon afault in a component or system. The HCP 5 monitors the torque-generativedevices, and determines the power output from the transmission 10required to achieve the desired output torque to meet the operatortorque request. As should be apparent from the description above, theESD 74 and the first and second electric machines 56 and 72 areelectrically-operatively coupled for power flow therebetween.Furthermore, the engine 14, the first and second electric machines 56and 72, and the electro-mechanical transmission 10 aremechanically-operatively coupled to transmit power therebetween togenerate a power flow to the output member 64.

As discussed above, managing output torque in order to maintaindrivability is a priority in controlling a hybrid powertrain. Any changein torque in response to a change in output torque request appliedthrough the transmission results in a change to the output torqueapplied to the driveline, thereby resulting in a change in propellingforce to the vehicle and a change in vehicle acceleration. The change intorque request can come from operator input, such a pedal positionrelating an operator torque request, automatic control changes in thevehicle, such as cruise control or other control strategy, or enginechanges in response to environmental conditions, such as a vehicleexperiencing an uphill or downhill grade. By controlling changes tovarious input torques applied to a transmission within a hybridpowertrain, abrupt changes in vehicle acceleration can be controlled andminimized in order to reduce adverse effects to drivability.

As is known by one having ordinary skill in the art, any control systemincludes a reaction time. Changes to a powertrain operating point,comprising the speeds and torques of the various components to thepowertrain required to achieve the desired vehicle operation, are drivenby changes in control signals. These control signal changes act upon thevarious components to the powertrain and create reactions in eachaccording to their respective reaction times. Applied to a hybridpowertrain, any change in control signals indicating a new torquerequest, for instance, as driven by a change in operator torque requestor as required to execute a transmission shift, creates reactions ineach affected torque generating device in order to execute the requiredchanges to respective input torques. Changes to input torque suppliedfrom an engine are controlled by an engine torque request setting thetorque generated by the engine, as controlled, for example, through anECM. Reaction time within an engine to changes in torque request to anengine is impacted by a number of factors well known in the art, and theparticulars of a change to engine operation depend heavily on theparticulars of the engine employed and the mode or modes of combustionbeing utilized. In many circumstances, the reaction time of an engine tochanges in torque request will be the longest reaction time of thecomponents to the hybrid drive system. Reaction time within an electricmachine to changes in torque request include time to activate anynecessary switches, relays, or other controls and time to energize orde-energize the electric machine with the change in applied electricalpower.

FIG. 3 graphically depicts reaction times of exemplary hybrid powertraincomponents to changes in torque request, in accordance with the presentdisclosure. Components to an exemplary hybrid powertrain systemincluding an engine and two electric machines are exemplified. Torquerequests and resulting changes in input torque produced by each torquegenerating device are illustrated. As described above, the data showsthat electric machines quickly respond to changes in torque requests,whereas the engine follows changes in torque requests more slowly.

A method is disclosed wherein reactions times of the engine and of theelectric machine or machines within a hybrid powertrain are utilized tocontrol in parallel an lead immediate torque request, controlling theengine, and an immediate torque request, controlling the electricmachines, the torque requests being coordinated by respective reactiontimes in order to substantially effect simultaneous changes to inputtorque.

Because, as discussed above, changes to input torque from the engine areknown to involve consistently longer reactions times than changes toinput torque from an electric machine, an exemplary embodiment of thedisclosed method can implement changes in torque request to the engineand the electric machine, acting in parallel as described above,including a lead period to the more quickly reacting device, theelectric motor. This lead period may be developed experimentally,empirically, predictively, through modeling or other techniques adequateto accurately predict engine and electric machine operation, and amultitude of lead periods might be used by the same hybrid powertrain,depending upon different engine settings, conditions, operating andranges and vehicle conditions. An exemplary equation that can be used inconjunction with test data or estimates of device reaction times tocalculate lead period in accordance with the present disclosure includesthe following:

T _(Lead) =T _(Lead Reaction) −T _(Immediate Reaction)   [1]

T_(Lead) equals the lead period for use in methods described herein.This equation assumes that two torque producing devices are utilized.T_(Lead Reaction) represents the reaction time of the device with thelonger reaction time, and T_(Immediate Reaction) represents the reactiontime of the device with the shorter reaction time. If a different systemis utilized, comprising for example, an engine with a long lead period,a first electric machine with an intermediate lead period, and a secondelectric machine with a short lead period, lead periods can be developedcomparing all of the torque generating devices. In this exemplarysystem, if all three torque generating devices are involved, two leadperiods, one for the engine as compared to each of the electricmachines, will be utilized to synchronize the responses in each of thedevices. The same system at a different time might be operating with theengine off and disengaged from the transmission, and a lead periodcomparing the first electric machine and the second electric machinewill be utilized to synchronize the responses in the two electricmachines. In this way, a lead period can be developed coordinatingreaction times between various torque generating devices can bedeveloped.

One exemplary method to utilize lead periods to implement paralleltorque requests to distinct torque generating devices in order to effectsubstantially simultaneous changes to output torque in response to achange in operator torque request includes issuing substantiallyimmediately a change to the engine torque immediate request, initiatingwithin the engine a change to a new engine output torque. This newengine output torque, in conjunction with the electric motor operatingstate, is still managed by the HCP in order to provide some portion ofthe total input torque to the transmission required to propel thevehicle. From the point that the engine torque immediate requestchanges, the lead period expires, described above taking into accountthe differences in reaction times between the engine and the electricmachine. After the lead period, a change to torque requests issued tothe electric machine or machines, managed by the HCP in order to fulfilla portion of the operator torque request, is executed, and the electricmachine changes the electric machine operating state, and as describedabove, the changes to the input torques provided by the engine and theelectric machine change substantially simultaneously.

As described in the disclosed method above, engine torque immediaterequests and torque requests to an electric machine are disclosed foruse in parallel to control distinct torque generative devices withdifferent reaction times to reaction to changes in operator torquerequest. Changes in operator torque request can include a simple changein desired output torque within a particular transmission operatingrange state, or changes in operator torque request can be required inconjunction with a transmission shift between different operating rangestates. Changes to operator torque requests in conjunction with atransmission shift are more complex than changes contained within asingle operating range state because torques and shaft speeds of thevarious hybrid powertrain components must be managed in order totransition torque applied from a first clutch and to a second previouslynot applied clutch without the occurrence of slip, as described above.

Shifts within a transmission, such as the exemplary transmission of FIG.1, frequently involve unloading a first clutch, transitioning through aninertia speed phase state, and subsequently loading a second clutch.Within the transmission of a conventionally powered vehicle utilizing anengine only, the change within a transmission from one fixed gear stateto another fixed gear state frequently includes unloading a firstclutch, allowing the vehicle to briefly coast, and then loading a secondclutch. However, as described in relation to FIG. 1 and Table 1, above,clutches within a hybrid powertrain transmission are frequently appliedin pairs or groups, and a shift within the transmission can involve onlyunloading one of the applied clutches and subsequently loading anotherclutch while maintaining engagement of a third clutch throughout theshift. FIG. 4 demonstrates gear transition relationships for anexemplary hybrid powertrain transmission, in particular as described inthe exemplary embodiment of FIG. 1 and Table 1, in accordance with thepresent disclosure. N_(I) is plotted against N_(O). At any fixed gearstate, N_(O) is determined by the corresponding N_(I) along the fixedgear state plots. Operation in either EVT Mode I or EVT Mode II, whereina continuously variable gear ratio is utilized to power from a fixedinput speed can take place in the respective zones illustrated on thegraph. Clutch states, C1-C4, as described in the exemplary embodiment ofFIG. 1, are described in Table 1. For instance, operation in a secondfixed gear state requires clutches C1 and C2 to be applied or loaded andclutches C3 and C4 to be not applied or unloaded. While FIG. 4 describesgear transitions possible in the exemplary powertrain illustrated inFIG. 1, it will be appreciated by one having ordinary skill in the artthat such a description of gear transitions is possible for anytransmission of a hybrid powertrain, and the disclosure is not intendedto be limited to the particular embodiment described herein.

FIG. 4 can describe operation of an exemplary system in a fixed gearstate or EVT mode, as described above, and it can also be used todescribe shift transitions between the various transmission operatingrange states. The areas and plots on the graph describe operation of theoperating range states through transitions. For example, transitionsbetween fixed gear states within an EVT mode region require transitoryoperation in the EVT mode between the fixed gear states. Similarly,transition from EVT Mode I to EVT Mode II requires a transition throughthe second fixed gear state, located at the boundary between the twomodes.

In accordance with FIGS. 1 and 4 and Table 1, an exemplary transmissionshift from a third fixed gear state to a fourth fixed gear state isfurther described. Referring to FIG. 4, both the beginning and thepreferred operating range states exist within the area of EVT Mode II.Therefore, a transition from the third gear state to the fourth gearstate requires first a shift from the third fixed gear state to EVT ModeII and then a shift from EVT Mode II to the fourth fixed gear state.Referring to Table 1, a hybrid powertrain transmission, beginning in athird fixed gear state, will have clutches C2 and C4 applied. Table 1further describes operation in EVT Mode II, the destination of the firstshift, to include clutch C2 applied. Therefore, a shift from the thirdfixed gear state to EVT Mode II requires clutch C4 to be changed from anapplied to a not applied state and requires that clutch C2 remainapplied. Additionally, Table 1 describes operation in the fourth fixedgear mode, the destination of the second shift, wherein clutches C2 andC3 are applied. Therefore, a shift from EVT Mode II to the fourth fixedgear state requires clutch C3 to be applied and loaded and requires thatclutch C2 remain applied. Therefore, clutches C4 and C3 are transitionedthrough the exemplary shift, while clutch C2 remains applied andtransmitting torque to the driveline throughout the shift event.

Applied to the methods disclosed herein, changes in input torque througha transmission shift can be adjusted to reduce negative effects todrivability by coordinating signal commands to various torque generativedevices based upon reaction times of the various components. Asdescribed above, many transmission shifts can be broken down into threephases: a first torque phase, during which an initially applied clutchis changed from a torque-bearing, locked, and synchronized clutch stateto an unlocked and desynchronized clutch state; an inertia speed phase,during which affected clutches are unlocked and in transitional states;and a second torque phase, during which a second previously not appliedclutch is changed from an unlocked and desynchronized clutch state to atorque-bearing, locked, and synchronized clutch state. Asaforementioned, clutch slip is preferably avoided throughouttransmission shifts to avoid adverse effects on drivability, and clutchslip is created when reactive torque applied across a clutch exceeds theactual torque capacity of the clutch. Therefore, within a transmissionshift event, input torques must be managed in relation to the actualtorque capacity of the currently applied clutch, such that thetransmission shift can be accomplished without the occurrence of slip.

While a process can be utilized to perform necessary steps in a clutchloading or unloading event in sequence, with the torque capacity of theclutch being maintained in excess of reactive torques, time involved inan unlocking transition is also important to drivability. Therefore, itis advantageous to perform associated torque requests and clutchcapacity commands in parallel while still acting to prevent slip. Suchparallel implementation of control changes intending to effect clutchstate changes associated with a transmission shift preferably occur inas short of a time-span as possible. Therefore, coordination of torquecapacity within the clutches involved in the transmission shift to thetorque requests, both to the engine and to the electric machine, asdescribed in the exemplary embodiment above, is also important tomaintaining drivability through a transmission shift. FIGS. 5-7 depictexemplary processes combining to accomplish an exemplary transmissionshift, in accordance with the present disclosure.

FIG. 5 is a graphical representation of torque terms associated with aclutch through an exemplary transitional unlocking state, in accordancewith the present disclosure. Lines illustrated at the left extreme ofthe graph depict clutch operation in a locked state. The graph depictsclutch command torque by a clutch control system and a resultingestimated torque capacity. Clutch torque capacity in a clutch resultingfrom a command torque is a result of many factors, including availableclamping pressure, design and conditional factors of the clutch,reaction time in the clutch to changes in the clutch control system. Asdemonstrated in the exemplary data of the graph in the initial lockedregion, it is known to command a torque to a locked clutch in excess ofthe clutch capacity and allow the other factors affecting the clutch todetermine the resulting clutch capacity. Also at the left extreme of thegraph depicting clutch operation in a locked state, estimated reactivetorque applied to the clutch as a result of input torque from the engineand electric machine torques is depicted. At the time labeled “InitiateUnlocking State”, logic within the clutch control system or the TCM,having determined a need to transition the clutch from locked tounlocked states, changes the command torque to some level lower than thetorque capacity but still higher than the reactive torque currentlyapplied to the clutch. At this point, mechanisms within the clutchcontrol system, for example, variable pressure control solenoids withinan exemplary hydraulic clutch control system, change settings tomodulate the clamping force within the clutch. As a result, torquecapacity of the clutch begins to change as the clamping force applied tothe clutch changes. As discussed above, the clutch reacts to a change incommand torque over a reaction time, and reaction time for a particularclutch will depend upon the particulars of the application. In theexemplary graph of FIG. 5, torque capacity reacts to a reduction incommand torque and begins to reduce accordingly.

As mentioned above, during the same unlocking state, reactive torqueresulting from input torque and electric machine torques must also beunloaded from the clutch. Undesirable slip results if the reactivetorque is not maintained below the torque capacity throughout theunlocking state. Upon initiation of the unlocking state, atsubstantially the same point on FIG. 5 where the torque capacity isreduced to initiate the unlocking state, limits are initiated andimposed upon input torques from the engine and the electric machine inorder to accomplish a ramping down of each to zero. As described in themethod disclosed herein and in exemplary embodiments described above,changes to limits including a engine torque immediate request and animmediate torque request are executed in a coordinated process,implementing a lead period calibrated to the reaction times of thevarious torque providing devices, such that the resulting input torquesfrom the devices are reduced substantially simultaneously. FIG. 5illustrates a method to perform this coordinated change to torquerequests by imposing limits upon torque requests in the form of a clutchreactive torque lead immediate min/max constraining the engine torqueimmediate request and a clutch reactive torque immediate min/maxconstraining the torque request to the electric machine. These maximumreactive torque values represent the maximum torque that is permitted tobe commanded from each torque providing device: the actual engine torqueimmediate request and the actual immediate torque request can be lessthan the maximum reactive torque values, but as the maximum valuesreduce, so the actual torque request values will also eventually reduce.The input torques from the engine and electric machine together provide,each up to the defined maximum values, some portion of the overall inputtorques, with the portion of each being controlled by the HCP. As aresult of the calibrated lead period, both the clutch reactive torquelead immediate min/max and the clutch reactive torque immediate min/maxreduce applied reactive torque to the clutch at substantially the sametime, resulting in the reduction to the actual clutch reactive torque asillustrated in FIG. 5. As will be appreciated by one having ordinaryskill in the art, other safeguards will additionally need to be utilizedto ensure that the torque capacity remains in excess of the reactivetorque throughout the unloading process. Many such methods arecontemplated, and an exemplary set of terms which might be used aredepicted on FIG. 5. For instance, a calibrated offset term can be usedto ensure that the command setting the clutch capacity remains in excessof the actual clutch reactive torque until the actual torque passesbelow some threshold. An exemplary threshold for such a purpose isdefined in FIG. 5 as the calibrated threshold for reactive torque. Inmaintaining this torque capacity request above the actual clutchreactive torque, and remembering that all devices include a reactiontime to request changes, including the clutch clamping mechanism, thedelay in the change to torque capacity in response to clutch commandchanges in combination with this offset term will maintain the torquecapacity in excess of the actual clutch reactive torque. Additionally,another threshold, a calibrated threshold for torque estimate, can beused to define the end of the torque phase. For instance, if an estimateof the clutch torque capacity, as determined by an algorithm modelingclutch operation, stays below this threshold through a calibrated periodof time, then the clutch can be determined to be in an unlocked state.

FIG. 6 is a graphical representation of torque terms associated with aclutch through an exemplary transitional locking state, in accordancewith the present disclosure. As described above, within manytransmission shift events, a second clutch is synchronized and locked,and torque is applied to the clutch. Lines illustrated at the leftextreme of the graph depict clutch operation in an unlocked state. Theinitiation of locking state requires a series of subordinate commandsnecessary to transition the clutch from an unlocked state to a lockedstate. As described above in relation to a transition to a second torquephase within a transmission shift, the clutch, including the shaftconnected to the oncoming torque providing shafts and the shaftconnected to the output member, must be synchronized. Once the clutchconnective surfaces attached to these shafts have been attenuated andare moving at the same rotational velocity, clamping force can begin tobe applied to the clutch to bring the clutch to a locked state and beginincreasing the torque capacity of the clutch. As described above withregards to avoiding slip during a torque phase, clutch capacity must beincreased before reactive torque to the clutch can be increased. Inorder to enable the application of input torques resulting in a reactivetorque across the clutch as rapidly as possible, an increase in clutchcapacity can be commanded anticipatorily to achieve an initial increasein clutch capacity coincident with the clutch reaching a locked state.Reactive torques, taking into account reaction times by utilizing a leadperiod by the method disclosed herein, can then be timely commanded witha short lag to follow increasing clutch torque capacity. An exemplaryembodiment of this method, acting in reverse of the limits imposed totorque requests as described in FIG. 5, imposes limits upon the torquerequests which can be issued to the engine and to the electric machineaccording to a calibrated ramp rate, selected to avoid slip. As depictedin FIG. 6, an clutch reactive torque immediate min/max acting as aconstraint upon electric machine torque requests is increased after acalibrated lead period from the initiation of an increasing clutchreactive torque lead immediate min/max acting as a constraint uponengine torque requests. By utilizing the lead period, the increase ininput torques from the engine and the electric machine increase reactivetorque applied to the clutch substantially simultaneously, according tothe methods disclosed herein. As the limits upon the torque generatingdevices are lifted according to the calibrated ramp rate applied to eachlimit, the HCP can command the engine and the electric machine tofulfill a portion of the reactive torque required from the clutch, eachup to the respective maximum. In this way, torque requests to the engineand the electric machine are coordinated in order to compensate forreaction times in order to increase input torques from eachsubstantially simultaneously through a shift event.

The calibrated ramp rate utilized in the above exemplary transmissionshift is a selected value which will adjust input torque levels to thedesired range quickly, but also will stay below the torque capacity forthe clutch so as to avoid slip. The ramp rate may be developedexperimentally, empirically, predictively, through modeling or othertechniques adequate to accurately predict engine and electric machineoperation, and a multitude of ramp rates might be used by the samehybrid powertrain, depending upon different engine settings, conditions,or operating ranges and behavior of the control system actuating theclutch torque capacity. The ramp rate used to decrease input torques inan unlocking event can but need not be an inverse of the ramp rate usedto increase input torques in a locking event. Similarly, the lead periodused to coordinate input torques can but need not be the same time spanvalue utilized in both transmission transitional states and can bevaried according to particular behaviors of a vehicle and itscomponents.

As described above, during a transmission shift, for example, betweentwo fixed gear states as defined in the exemplary transmission describedabove, the transmission passes through an inertia speed phase between afirst torque phase and a second torque phase. During this inertia speedphase, the originally applied, off-going, clutch and the on-comingclutch to be applied are in an unlocked state, and the input isinitially spinning with a rotational velocity that was shared betweenclutch members across the first clutch just prior to becomingdesynchronized. In order to accomplish synchronization within the secondclutch to be applied and loaded in the second torque phase, inputs to beconnected to the second clutch must change N_(I) to match the drivelineattached through the transmission at some new gear ratio. Within a shiftin a hybrid powertrain transmission, shifts can occur through anoperating range state where at least one clutch is applied while anotherclutch is about to be transitioned to a locked state, but remainsdesynchronized. Operation of a transmission in a variable, non-fixedstate, such as exemplary EVT Mode I and EVT Mode II described above,allows for a variable ratio of input and output speeds. Therefore,utilizing one of the EVT modes as a transitory state through an inertiaspeed phase, N_(I) can be transitioned from an initial speed to a targetspeed while maintaining transmission of T_(O).

An exemplary method to accomplish this synchronization through aninertia speed phase of a transmission shift is graphically depicted inFIG. 7, in accordance with the present disclosure. The effects of thetransmission shift upon two terms descriptive of the shifting processare illustrated in two sections with a common timescale. The top sectiondepicts N_(I), initially connected through the first, initially appliedclutch. The upper dotted line represents the velocity profile of N_(I)while the first clutch is in a locked state before initiation of theshift. The bottom dotted line represents the velocity profile of N_(I)that must be achieved to synchronize N_(I) with the output speed of thesecond clutch. The transition between the two dotted lines representsthe change to input speed that must take place to accomplish the shift.The bottom section of FIG. 7 depicts input acceleration (N_(I) _(—)_(DOT)), or a derivative with respect to time of N_(I). N_(I) _(—)_(DOT) is described in this case as the input acceleration immediateprofile or the acceleration profile driven with a relatively quickreaction time by an electric machine or machines, and the term closelytracks actual N_(I) _(—) _(DOT). The input acceleration immediateprofile shows the change in the rate of speed which must be accomplishedin order to transition the N_(I) from an initial N_(I) at thesynchronous state with the first clutch to a target input speed at thesynchronous state with the second clutch. The initial flat portiondescribes the acceleration with which the input speed is increasedbefore the initiation of the shift, and this constant value reflects theslope of the input speed in the left portion of the top section of theFIG. 7. At the time of the initiation of the shift, based upon operatorinput such as pedal position and algorithms within the transmissioncontrol system, including determining a preferred operating range state,a determination is made regarding target input speed that will berequired to achieve synchronization and the target input accelerationprofile required to produce the requisite change in N_(I). A targetinput speed_(—) _(DOT) based upon N_(O) and the target operating rangestate after the shift is completed, can be termed an input accelerationlead predicted profile and describes the N_(I) _(—) _(DOT) that needs toexist after the inertia speed phase is completed. A method is disclosedto define an input acceleration immediate profile to effect changes inN_(I) in accordance with a synchronous shift through an inertia speedphase.

A profile defining N_(I) _(—) _(DOT) through an inertia speed phase isconfined by a number of variables. As described above, an initial N_(I)value and N_(I) _(—) _(DOT) value can be monitored or described at theoutset of the shift. A target input speed value and N_(I) _(—) _(DOT)value can be described based upon a desired operating range state,N_(O), and a measure of powertrain operation, such as a pedal position.Constraints for the transition between the initial values and the targetvalues include physical characteristics of the engine in response toengine commands and desired times to complete shifts. Changes to N_(I)solely as a result of engine operation can span from wide-open throttleaggressively increasing N_(I) to completely cutting output of the engineaggressively decreasing N_(I). Engine commands can be modulated betweenthese extreme engine commands for resulting changes to N_(I) based upondesired shift characteristics. Changes to engine output can beaccomplished traditionally through changes to throttle settings.However, one having skill in the art will appreciate that such throttlechanges require large lead times, as described above, associated withthe mechanical changes that occur when an engine receives changes inengine commands. Alternatively, in a situation where engine output needsto be modulated by some moderate amount and for a transitory period, amethod is known whereby either spark timing can be retarded or fuelinjection timing can be advanced to reduce engine output through acombustion cycle. While this method achieves changes to engine outputmore quickly than changes to throttle commands and allows for theprevious output of the engine to be quickly restored, such changesreduce fuel efficiency by transferring less of the energy of combustionto work on the piston. However, in transitory periods such as a shiftrequiring moderate changes in N_(I), changes to engine output throughspark or injection changes can be preferable. Additionally, an electricmachine or machines can be used to either boost engine output or assistin pulling down engine speed through hybrid powertrain methods describedabove.

Constraints for the transition between the initial values and the targetvalues also include desired times to complete shifts. A total desiredspeed phase time can be defined based upon the context of powertrainoperation, for example, as described by an accelerator pedal position.For instance, a shift with a fully depressed accelerator pedal (100%pedal) implies a desire by an operator to accomplish shifts and anyassociated decrease in T_(O) as quickly as possible. A shift through a0% pedal coast-down downshift implies that shift times can be relativelylonger without adversely affecting drivability. Additionally, an initialinput speed delta can be used to describe the degree of change in N_(I)required to accomplish the desired shift. The initial input speed deltadescribes a difference between the input speed at the instant theinertia speed phase is initiated versus an input speed that would berequired in at that instant if the powertrain were already in thedesired operating range state. An exemplary initial input speed delta isillustrated in FIG. 7. Greater initial input speed deltas imply thatgreater changes to N_(I) will need to occur through the inertia speedphase, requiring either more drastic changes to engine output or greatertotal desired speed phase times.

An exemplary method to set total desired speed phase time based uponaccelerator pedal position and initial input speed delta includes use ofa calibrated 2D look-up table. FIG. 8 illustrates in tabular form use ofan exemplary 2D look-up table to determine inertia speed phase times, inaccordance with the present disclosure. Accelerator pedal position andthe initial N_(I) delta allow projection of a change required in N_(I),as describe above, which, in turn, allows estimation of an inertia speedphase time. Based upon the given inputs, an estimated inertia speedphase time can be estimated. Values of the initial N_(I) delta in thelook-up table can span positive and negative values, allowing fordifferent calibrations according to upshifts and downshifts.

Once behavior of N_(I) at the initiation of the inertia speed phase,behavior of a target input speed based upon a desired operating rangestate, and a total desired speed phase time are established, atransition described by a input acceleration immediate profile can bedescribed. As will be appreciated based upon any comparison of N_(I)values versus time, wherein different operating range states havedifferent projections of N_(I) based upon N_(O), as is described by thedotted lines in the N_(I) portions of FIG. 7, inertia speed phase N_(I)curves are likely to take an S-shape, with transitory sub-phasestransitioning to and from the initial and target input speed and N_(I)_(—) _(DOT) values and a center sub-phase linking the sub-phases. Bydividing an inertia speed phase into three sub-phases, necessarytransitions to an input acceleration immediate profile can be described.FIG. 9 describes an exemplary inertia speed phase divided into threesub-phases, in accordance with the present disclosure. Sub-phase 1describes a transition from the initial N_(I) and N_(I) _(—) _(DOT)values. A time T_(I) for the sub-phase 1 or a first phase can becalculated through the following equation:

T ₁ =K ₁*TotalDesiredSpeedPhaseTime   [2]

wherein K₁ is a calibration between zero and one describing a desiredbehavior of N_(I). K₁ can be a variable term, set by indications of thecontext of powertrain operation describing required properties of theshift, or K₁ can be a fixed calibrated value. Sub-phase 3 describes atransition to the target input speed and N_(I) _(—) _(DOT) values. Atime T₃ for the sub-phase 3 or a third phase can be calculated throughthe following equation:

T ₃ =K ₃*TotalDesiredSpeedPhaseTime   [3]

wherein K3 is a calibration between zero and one describing a desiredbehavior of N_(I) and can be set by methods similar to K₁. Sub-phase 2describes a transition between sub-phases 1 and 3. A time T₂ or a secondphase, as the remaining portion of the total desired speed phase time tobe set after T₁ and T₃ are defined, can be calculated through thefollowing equation:

T ₂=TotalDesiredSpeedPhaseTime−T ₁ −T ₃   [4]

Sub-phase 2 is depicted as a straight line in the exemplary data of FIG.9. It will be appreciated that a curved transition can be defined in thesub-phase 2 region depending upon the total desired speed phase time andthe behavior of the exemplary powertrain. However, a straight line asdepicted can be preferable. The slope of the N_(I) curve in sub-phase 2describes the peak speed phase input acceleration that must be achievedin order to accomplish the desired inertia speed phase in the totaldesired speed phase time. In the exemplary method where N_(I) _(—)_(DOT) through sub-phase 2 is a constant value, this peak speed phaseinput acceleration can be calculated through the following equations:

$\begin{matrix}{{{PeakSpeedPhaseInputAccel}.} = {\frac{K_{\alpha}*\left( {N_{I\_ TARGET} - N_{I\_ INIT}} \right)}{TotalDesiredSpeedPhaseTime} + K_{\beta}}} & \lbrack 5\rbrack \\{K_{\alpha} = \frac{1}{1 - \frac{K_{1}}{2} - \frac{K_{3}}{2}}} & \lbrack 6\rbrack \\{K_{\beta} = {K_{\alpha}*\frac{K_{1}}{2}}} & \lbrack 7\rbrack\end{matrix}$

By describing behavior of N_(I) _(—) _(DOT) required through stages ofthe inertia speed phase, an input acceleration immediate profile can bedefined to operate N_(I) changes in an inertia speed phase.

As described above, reaction times in engines to control commands tendto be slow relative to reaction times of other components of apowertrain. As a result, engine commands issued to an enginesimultaneously to an input acceleration immediate profile would includea resulting lag in changes to N_(I). Instead, a method is additionallydisclosed, wherein an input acceleration lead immediate profile isdefined based upon a lead period describing the reaction time of theengine. Such a lead period can be the same lead period as calculated inequation (1) above or can be calculated separately based upon thespecific behavior of the engine in an inertia speed phase. For instance,because there is no direct implication of electric machine operation inN_(I) _(—) _(DOT), the lead period for the input acceleration leadimmediate profile can include a factor for an electric machine helpingto change N_(I) _(—) _(DOT) more quickly than the engine could inisolation. The input acceleration lead immediate profile depicted inFIG. 7 includes a portion of the lead profile before the start of theinertia speed phase. In the case of a shift from a fixed gear state,wherein after a shift is initiated, an unlocking event in an off-goingclutch must occur, the time period during the unlocking event provides aperiod wherein commands can be issued to the engine in advance of adesired change in N_(I). This lead in advance of the inertia speed phaseis beneficial in maintaining inertia speed phases to a total desiredspeed phase time, in accordance with the determinations described above.In circumstance where no or an insufficient lead period is available toallow an input acceleration lead immediate profile to effect enginechanges according to the input acceleration immediate profile, anadjustment can be made to the inertia speed phase to compensate for thereaction time of the engine and the resulting lag in changes to N_(I).Circumstances where no lead is possible includes a shift starting froman exemplary EVT mode, wherein only one clutch is initially engaged, andthe inertia speed phase can start immediately upon command. In such acircumstance, the initiation of the inertia speed phase can be delayedafter commands are issued to the engine in accordance with thedetermined lead time.

The above methods describe torque management processes as a comparisonof positive values. It will be appreciated by one having ordinary skillin the art that clutch torques are described as positive and negativetorques, signifying torques applied in one rotational direction or theother. The above method can be used in either positive or negativetorque applications, where the magnitudes of the torques are modulatedin such a way that the magnitude of the applied reactive torque does notexceed the magnitude of the torque capacity for a particular clutch.

FIG. 10 graphically illustrates an exemplary inertia speed phase whereinan input acceleration immediate profile is affected by imposition of aminimum input acceleration constraint in accordance with the presentdisclosure. In the exemplary operation of a transmission shift, aninstance is depicted in which an input acceleration lead immediateprofile has been determined for engine control through an inertia speedphase, and additionally, a corresponding input acceleration immediateprofile has been determined for electric machine control through theinertia speed phase. Two sections are depicted in FIG. 10, including atop section depicting input speed against time and a bottom sectiondepicting input acceleration against time, with the two sections sharinga common timescale. In an instance where negative N_(I) _(—) _(DOT) ordeceleration is occurring to the engine in an inertia speed phase, thiscondition is most commonly an instance where the engine is simply beingallowed to slow down by internal frictional and pumping forces withinthe engine. However, when an electric machine is decelerating, thiscondition is most commonly accomplished with the electric machine stillunder power, or conversely, operating in a regeneration mode. Becausethe electric machine is still operating under system control and withimplications with the rest of powertrain's systems, the motor is stillsubject to systemic constraints, for instance, battery power availableto drive the motor. FIG. 10 imposes such a systemic constraint in theminimum input acceleration constraint. The effect of this constraintupon input speed can be seen in the top section of the graph, whereinthe straight section in the middle of the inertia speed phase isinterrupted with a flattened section. Where such a constraint interfereswith the input acceleration immediate, programming within the electricmachine control system modify the input acceleration immediate toaccommodate the constraint. In the present example, the inputacceleration immediate profile is impacted by the minimum inputacceleration constraint such that negative acceleration of the inputspeed is delayed. Once the constraint no longer limits electric machineoperation within the input acceleration immediate, the control systemoperates to recover the N_(I) _(—) _(DOT) to the effect the desiredchanges to N_(I).

As described above, a clutch designed for synchronous operation isfrequently operated under a control scheme through which clutch torquecapacity is always maintained in excess of the reactive torquetransmitted through the clutch in order to avoid slip. In exemplaryshifts described above, such schemes frequently unload and load clutchesin isolated events, preserving the zero slip condition through each ofthe isolated events. Use of an inertia speed phase is also disclosed, inwhich the speed of an input member, N_(I), is changed from a speedsynchronous with an off-going clutch to a speed synchronous with anon-coming clutch. N_(I) can be changed by applying torque through any ofthe torque generative devices attached to the input member. For example,an electric machine or machines can apply a torque to the input memberto change N_(I). Alternatively or additionally, an engine can changeoutput torque to change the speed of the input member. Electric machinescan frequently change T_(A) and T_(B) quickly and efficiently. Undercertain circumstances, the electric machines can apply a negative torqueand act in a generator role, providing energy to an energy storagedevice for later use. However, torque applied by the electric machinescan be limited by a number of factors, including electric machinecapabilities, energy storage device limitations, and other limitingschemes operating to protect the powertrain. Engines, on the other hand,are slower to change torque applied to the input member. T_(I) can bereduced according to a faster control method, such as changing spark orinjection timing changes to temporarily reduce combustion efficiency, orchanged according to a slower method, such as throttle changes. Fasterengine control methods decrease effects to drivability by making moreresponsive changes and recover relatively quickly from the changes toT_(I) to an original level, but decrease overall fuel efficiency. Slowerengine control methods are significantly less responsive, requiring amultitude of changes within the combustion cycle of the engine to changethe resulting T_(I) from the engine. Additionally, changes to restoreT_(I) after a throttle change are similarly unresponsive to the originalchange, requiring a throttle change to the new setting. Changes toengine torque, either through faster engine control methods or slowerengine control methods, cause changes to powertrain output and impactsto drivability.

As described above, particular clutch designs, although optimallyutilized in synchronous operation wherein substantially zero slip ismaintained, can additionally be utilized to provide for controlledoperation with some degree of slip. A method is disclosed to performcontrolled asynchronous, clutch assisted shifts through an oncomingclutch in order to provide assistance to changing N_(I) whiletransmitting torque to an output shaft through an inertia speed phase.This disclosure intends to distinguish between asynchronous shiftsnormally used in transmission shift and the use of normallysynchronously operated clutches in an asynchronous clutch assisted shiftmethod. For reasons of simplicity, throughout the methods disclosedherein, these shifts will be referred to as asynchronous shifts, but itwill be appreciated that the shifting method described throughout themethods are clutch assisted shifts. By advancing a touching state andsubsequent clamping force on an oncoming clutch in an otherwisesynchronous shift, as described above, a clutch torque (‘T_(C)’) can beutilized to affect changes to N_(I) and T_(O). Through the applicationof the oncoming clutch, power from the output member in the form of areactive torque through the oncoming clutch can be used to bring N_(I)closer to the target input speed. As will be appreciated by one havingordinary skill in the art, this utilization of power from the outputmember will affect the torque of the output member and, therefore, willaffect drivability. However, affects to drivability cause by generationof T_(C) will frequently be less severe than affects to drivabilityresulting from changes to engine commands and, additionally, includenone of the negative affects of commanding the engine back to normallevels after the shift. As a result, changes to N_(I) according to adisclosed method are preferably affected by T_(A) and T_(B), thenadditionally by T_(C), as needed. Changes can additionally be affectedby T_(I) as needed in the event T_(A), T_(B), and T_(C) are fullyutilized.

FIGS. 11 and 12 graphically contrast an exemplary synchronous shift andan asynchronous, clutch assisted shift utilized to provide T_(C) throughthe shift, in accordance with the present disclosure. FIG. 11 is anexemplary synchronous shift, as described in the exemplary embodimentsdisclosed herein. An input speed, defined at the outset by an initiallyengaged gear state and described by N_(O)*GR_(INITIAL), transitionsthrough an inertia speed phase to a line defined by a destination gearstate described by N_(O)*GR_(DESTINATION). As described in FIG. 5 above,an off-going clutch transmitting T_(CR-OFFGOING) transitions from somenormally transmitted reactive torque level to zero through a torquephase. Additionally, as described in FIG. 6 above, an oncoming clutchtransmitting T_(CR-ONCOMING) transitions from zero to some normallytransmitted reactive torque level through a second torque phase. In theperiod between the torque phases, an inertia speed phase takes place inwhich the input speed is changed from some speed set by the initial gearstate to a speed set by the destination gear state. T_(O) and N_(O)remain largely unaffected by the changes in the inertia speed phase dueto torque sustained through the transmission by a third, constantlyengaged, clutch. Operated according to the methods described herein, asynchronous shift performed in this way provides for a change betweenengaged gears with a minimal impact to drivability.

FIG. 12 is an exemplary asynchronous, clutch assisted shift to provideT_(C) through the shift in order to assist changes to N_(I) and T_(O). Ashift through a shift event is defined, and a determination is madethat, based upon adjusting N_(I) as required through the input speedprofile with electric machine torque, T_(O) will fall below desiredlevels. Application of T_(C) is determined to be appropriate, so clutchreactive torque is transmitted through the oncoming clutch within theinertia speed phase. The reactive clutch torque transmitted through theoncoming clutch acts as T_(C) to change N_(I) toward the target inputspeed. In this way, torque transmitted through an oncoming clutch can beutilized to assist in changing N_(I) and T_(O) through a transmissionshift.

In an inertia speed phase in an exemplary system utilizing a pluralityof planetary gear sets as described in FIG. 1 and maintaining T_(O)through the inertia speed phase through maintaining a locked clutch inan EVT mode through the speed phase, N_(I) and T_(O) are related.Changing N_(I) through the inertia speed phase, for example, reducingN_(C) to zero, while maintaining a desired T_(O) (‘T_(O) _(—)_(DESIRED)’) requires manipulation of other terms through the inertiaspeed phase. In the exemplary system described above, the system torquebalance can be expressed by the following equation.

$\begin{matrix}{\begin{bmatrix}N_{I\_ DOT} \\T_{O}\end{bmatrix} = {{\begin{bmatrix}M_{11} & M_{12} \\M_{21} & M_{22}\end{bmatrix}\begin{bmatrix}T_{A} \\T_{B}\end{bmatrix}} + {\begin{bmatrix}C_{1} \\C_{2}\end{bmatrix}T_{C}} + {\begin{bmatrix}E_{1} \\E_{2}\end{bmatrix}T_{engine}}}} & \lbrack 8\rbrack\end{matrix}$

This relationship can be manipulated by one having ordinary skill in theart to express the following equation.

$\begin{matrix}{\begin{bmatrix}T_{I} \\T_{O}\end{bmatrix} = {{\begin{bmatrix}M_{11} & M_{12} \\M_{21} & M_{22}\end{bmatrix}\begin{bmatrix}T_{A} \\T_{B}\end{bmatrix}} + {\begin{bmatrix}N_{11} & N_{12} \\N_{21} & N_{22}\end{bmatrix}\begin{bmatrix}N_{I\_ DOT} \\N_{O\_ DOT}\end{bmatrix}} + {\begin{bmatrix}C_{1} \\C_{2}\end{bmatrix}T_{C}}}} & \lbrack 9\rbrack\end{matrix}$

N_(I DOT), the desired change to input speed through the inertia speedphase, can be treated as a given for the purposes of determining systemchanges required to affect the required input speed profile. Changes toT_(I) and T_(O) through a shift can be described by the torque inputs bythe various torque generating devices, by a description of accelerationsin the input and the output members, and by describing T_(C). Theseterms can be combined and expressed as the following.

$\begin{matrix}{\begin{bmatrix}T_{I} \\T_{O}\end{bmatrix} = {\begin{bmatrix}{T_{I}M} \\{T_{O}M}\end{bmatrix} + \begin{bmatrix}{T_{I}N} \\{T_{O}N}\end{bmatrix} + \begin{bmatrix}{T_{I}C} \\{T_{O}C}\end{bmatrix}}} & \lbrack 10\rbrack\end{matrix}$

Equation 11 states that T_(I) and T_(O) can be expressed according toterms expressing the effect of electric machines upon T_(I) (‘T_(I)M’),the effect of electric machines upon T_(O) (‘T_(O)M’), the effect ofN_(I) _(—) _(DOT) and N_(O) _(—) _(DOT) upon T_(I) (‘T_(I)N’), theeffect of N_(I) _(—) _(DOT) and N_(O) _(—) _(DOT) upon T_(O) (‘T_(O)N’),the effect of T_(C) upon T_(I) (‘T_(I)C’), and the effect of T_(C) uponT_(O) (‘T_(O)C’). Further, for the purpose of evaluating TC, the effectsof the electric machines, N_(I) _(—) _(DOT), and N_(O) _(—) _(DOT) uponthese terms can be collectively described as T_(I)X and T_(O)X terms,resulting in the following equation:

$\begin{matrix}{\begin{bmatrix}T_{I} \\T_{O}\end{bmatrix} = {\begin{bmatrix}{T_{I}X} \\{T_{O}X}\end{bmatrix} + \begin{bmatrix}{T_{I}C} \\{T_{O}C}\end{bmatrix}}} & \lbrack 11\rbrack\end{matrix}$

In this way, T_(O) can be described in terms of T_(O)X through a shift,in particular with respect to a T_(O)X_(MAX) in a given shift, andcompared to T_(O) _(—) _(DESIRED) for that shift. This comparison yieldsa discrepancy that must be filled in order to maintain T_(O) _(—)_(DESIRED) through the shift. This discrepancy can be used to calculateT_(C) through the shift in order to generate a T_(O)C to match theidentified discrepancy.

FIG. 13 graphically illustrates exemplary use of output torque termsdescribed herein through a transmission shift, in accordance with thepresent disclosure. Three portions of the graph represent T_(O), N_(C)for an oncoming clutch, and T_(O)C, respectively, against a commontimescale through an exemplary shift. The middle portion of the graphdepicts, as described above, that an input speed profile changing N_(C)from an initial value to zero can be assumed through the inertia speedphase. T_(O), subordinated in this exemplary method to the input speedprofile as a given to powertrain operation, is expressed as T_(O) _(—)_(DESIRED), and other terms are modulated to achieve an output torqueprofile as close to the defined T_(O) _(—) _(DESIRED) profile aspossible. T_(O) is described through an initial gear state, a torquephase, an inertia speed phase, and a second torque phase. T_(O) _(—)_(DESIRED) is described through the shift collectively by T_(O) _(—)_(GEAR1) _(—) _(DESIRED), T_(O) _(—) _(TP) _(—) _(DESIRED), T_(O) _(—)_(SPEED) _(—) _(DESIRED), and T_(O) _(—) _(GEAR2) _(—) _(DESIRED),representing collectively a desired output torque profile through ashift. This desired output torque profile can be calibrated based uponresulting acceleration of the output, shift feel, and other factorsaffected by T_(O). The shaped of the desired output torque profile cantake many shapes depending upon the desired shift-feel of thepowertrain. T_(O)X_(MAX), as described above, represents a maximumoutput torque that can be delivered by the electric machine or machinesbased upon current powertrain operation. Limiting factors inT_(O)X_(MAX) include available battery power and maximum electricmachine torques. As described herein, T_(C) can be utilized to provideadditional capability to change the input speed and maintain T_(O).Affects of T_(C) at a maximum upon T_(O), T_(O)C_(MAX), can be added toT_(O)X_(MAX) through the speed phase generating aT_(O)X_(MAX)+T_(O)C_(MAX) line or T_(O) _(—) _(MAX). This linerepresents a maximum capability of the electric machines and theoncoming clutch to provide output torque through the inertia speed phaseunder current powertrain operating parameters. Because input speedchange is preferably provided by electric machine torque, T_(O)X_(MAX)is maintained through the inertia speed phase and excess capacity tomaintain T_(O) is accomplished by reducing T_(C). T_(O)C_(MAX) can bevariable. For instance, constraints can act upon available clutchclamping force or clutch power limits can limit how much energy the oncoming clutch is allowed to generate. However, under unconstrainedoperation, T_(O)C_(MAX) can be a constant term through the inertia speedphase. The bottom portion of the graph illustrates T_(O)C values,collective describing a desired clutch torque profile, resulting fromthe portion of T_(O)C_(MAX) utilized to achieve the desired outputtorque profile. These values can be converted into T_(C) commandsthrough the inertia speed phase of the shift. By modulating T_(C)commands through the speed phase, collectively forming a clutch torqueprofile, T_(O) _(—) _(DESIRED) can be maintained through the shift. Inthe event T_(O) _(—) _(DESIRED) cannot be maintained throughout theshift through the electric machines and the clutch assisted shift, ameasure of output torque deficiency, for example an output torquedeficiency profile, can be described and input torque can be utilized tospan the deficiency.

A control method can be defined utilizing the profiles described in FIG.13 utilizing a defined factor to set output torque to T_(O) _(—)_(DESIRED). A gamma factor can be described, wherein gamma equals onedescribed T_(O) equal to T_(O) _(—) _(DESIRED). By defining a gammaterm, programming within a powertrain control system can defined toaccommodate or simplify determination and modulation of T_(O) incomparison to T_(O) _(—) _(DESIRED) through shift events.

Limits on T_(O), T_(I), and T_(C) must be observed in the control ofT_(C). T_(O)X_(MAX) represents the most torque that the electric motorscan produce. T_(O)C_(MAX) represents the most torque that the oncomingclutch can impart. T_(I) _(—) _(MAX) represents the capacity limit ofthe engine to apply torque. FIG. 14 graphically illustrates exemplaryuse of input and output torque terms including limiting terms through atransmission shift, in accordance with the present disclosure. T_(O),T_(I), and T_(C) are depicted against a common timescale through anexemplary shift. The top portion of the graph describes a desired outputtorque profile similarly to the top portion of FIG. 13, except that, asdescribed above, the profile of FIG. 14 takes a different shape than theprofile of FIG. 13 according to a desired shift-feel for the powertrain.T_(O)X_(MAX) and T_(O)C_(MAX) are depicted, including a resulting T_(O)_(—) _(MAX) line describing the limit of the electric machine ormachines and the oncoming clutch to affect T_(O). T_(C) is preferablycommanded to maintain the desired output torque profile, but is limitedby the T_(O) _(—) _(MAX) line such that the lesser of the desired outputtorque profile and the T_(O) _(—) _(MAX) lines a defines desired clutchtorque profile according to the T_(O) domain. However, these desiredT_(O)C commands, collectively described as a desired clutch torqueprofile, must be converted from the T_(O)C domain into the T_(C) domainaccording to the relationships described in Equations 11-13 and thenlimited according to system constraints.

Limitations based upon T_(I) and T_(C) must be determined and used toconstrain resulting T_(C) commands. The middle portion of the graphdepicts limitations based upon T_(I). T_(I) _(—) _(MAX) represents anengine capacity limit or how much torque the engine can apply withoutviolating engine torque limits. T_(I)@T_(O)X_(MAX) describes T_(I)present when T_(O)X_(MAX) is applied. T_(I)C_(MAX) describes T_(I)present when T_(O)C_(MAX) is applied. The sum of these two valuesrepresents T_(I) resulting from the electric machine or machines and theoncoming clutch. Two exemplary T_(O)C_(MAX) curves are described.Example one describes T_(I)C_(MAX) values a lesser magnitude. Thesevalues do not cause violation of the T_(I) _(—) _(MAX) line, and,therefore, no modification to corresponding T_(C) values is required.Example two describes T_(I)C_(MAX) values a greater magnitude. Thesevalues do violate the T_(I) _(—) _(MAX) line. Corresponding T_(C) valuesmust be reduced in order to create reductions in T_(I)C values. Thebottom portion of the graph depicts limits imposed upon T_(C) commands.T_(I) _(—) _(MAX) from the middle portion of the graph is depicted inthe T_(C) domain. Additionally, T_(C) _(—) _(MAX) _(—) _(ENERGY) isdepicted, describing an energy limit upon the clutch. Such an energylimit through a speed phase can be described by the following equation.

$\begin{matrix}{{TotalClutchEnergy} = {\int_{0}^{SpeedPhaseTime}{T_{{C\_ MAX}{\_ ENERGY}}*N_{C}*{t}}}} & \lbrack 12\rbrack\end{matrix}$

It will be appreciated that energy will have to managed for the entiretyof time in which controlled slip is utilized to generate T_(C). Anunderstanding or calibration of allowable clutch energy through a speedphase time allows a description of T_(C) _(—) _(MAX) _(—) _(ENERGY) as alimit to T_(C) that can be applied. For the purpose of determining alimit to T_(C), a constant value for T_(C) _(—) _(MAX) _(—) _(ENERGY)can be assumed, such that limiting T_(C) below throughout an inertiaspeed phase will ensure that the energy limit of the clutch is notviolated. Further, an N_(C) profile of a constant ramp down rate asdepicted in the middle portion of FIG. 13 can be assumed. Making theseassumptions, T_(C) _(—) _(MAX) _(—) _(ENERGY) can be calculated throughthe following equation.

$\begin{matrix}{T_{{C\_ MAX}{\_ ENERGY}} = \frac{2*{TotalClutchEnergy}}{N_{C}*{SpeedPhaseTime}}} & \lbrack 13\rbrack\end{matrix}$

Utilizing T_(C) _(—) _(MAX) _(—) _(ENERGY), a limit can be set to T_(C)such that the energy limit of the clutch will not be exceeded.Calculated in this way, T_(C) _(—) _(MAX) _(—) _(ENERGY) is depicted inthe bottom portion of FIG. 14. T_(I) _(—) _(MAX) and T_(C) _(—) _(MAX)_(—) _(ENERGY) are depicted as exemplary limits to T_(C), however, onehaving ordinary skill in the art will appreciate that other limits toT_(C) can additionally be utilized, depending upon the particular designof the powertrain. T_(C) _(—) _(LIMIT) can be derived from the lesser ofthe identified limits through the inertia speed phase, and an exemplaryresulting T_(C) _(—) _(LIMIT) is depicted. T_(C) commands resulting fromthe desired clutch torque profile and limited by T_(C) _(—) _(LIMIT)form the clutch torque profile. Additionally, a lead clutch torqueprofile based upon the clutch torque profile is formed for the purposeof engine torque control through a speed phase.

As a result of the above calculations, a T_(O) command profile can bedescribed to generate T_(C) commands. Such a profile is illustrated inFIG. 14 by a dotted line. Calculations to determine T_(O)C values foruse in generating T_(C) commands are generated based upon the commandprofile at some sample rate determined by the processors and programmingutilized to determine the values. As is known in the art, higher samplerates provide for more accurate control but require more processingpower. FIG. 14 further describes an exemplary determination of T_(O)Cvalues and the resulting sample rate of values generated. In theexemplary inertia speed phase, seven T_(O)C values are generated andprovide sufficient resolution for accurate control of T_(C). The samplerate can depend upon the speed phase time or may be a fixed valuecalibrated to be valid for a range of possible speed phase times.Particular sample rates may be developed experimentally, empirically,predictively, through modeling or other techniques adequate toaccurately predict powertrain operation, and a multitude of sample ratesmight be used by the same powertrain for different conditions oroperating ranges.

FIG. 15 illustrates an exemplary process by which a powertrain incontrolled through an inertia speed phase, utilizing oncoming clutchtorque to maintain an output torque, in accordance with the presentdisclosure. Process 500 starts in step 502. In step 504, methodsdescribed herein are employed to plan a pending desired transmissionshift. In order to generate a required input speed profile required tosynchronize the oncoming clutch, a speed phase time is estimated, forexample, by using table lookup based on pedal input, the initial anddesired destination operating range states of the desired shift, and theslip speed between a current input speed and a target input speed. Instep 506, desired powertrain operation is evaluated, for example, basedupon T_(O) _(—) _(REQ). Step 508 utilizes the desired powertrainoperation of step 506 to determine a desired output torque profile, forexample through a look-up table. This desired output torque profile canbe utilized as a gamma profile. Based upon the inputs to step 510 andspeed phase time developed in step 504, an input speed profile, an inputacceleration lead immediate profile, and an input acceleration immediateprofile are generated in step 510 defining the anticipated boundaries ofthe shift including the inertia speed phase. In step 512, capability ofthe electric machine or machines are evaluated based upon factorsdescribed herein and T_(O)X_(MAX) is defined. In step 514, capability ofthe oncoming clutch to provide torque is evaluated based upon factorsdescribed herein, including an estimation of clutch energy capacity, andT_(O)C_(MAX) is defined. In step 516, limits imposed by T_(I) based upondifferent factors including T_(I) _(MAX), T_(I) _(—) _(MIN), desiredoutput torque profile, T_(O)X_(MAX), and T_(O)C are determined. In step518, capabilities and limits from earlier steps are evaluated, and adesired clutch torque profile is generated. In step 520, both the clutchtorque and lead clutch torque commands are generated based upon thedesired clutch torque profile or the desired gamma output torqueprofile. The lead clutch torque command and lead input accelerationprofile are used to determine the optimal input speed command for ECMtorque control. Commands to the ECM and to the TCM are generated in step522. The clutch torque command is sent to transmission control modulefor proper clutch control to produce the desired torque capacity. BothECM and TCM will report the estimated engine and clutch torque produced,along with the N_(I) _(—) _(DOT) profile the torque determinationalgorithm will calculate the open loop motor torques. Combined with theclosed loop motor torques calculated using input speed profile through aPI controller, the final torque commands are then sent to the motorcontrollers for final torque production.

The above exemplary embodiments of shifts include shifts from a fixedgear operating range state to another fixed gear operating range state.However, it will be appreciated that the methods described herein can beutilized to shift to or from an EVT mode operating range state asdescribed above. For example, in a shift from a mode state to a fixedgear state, an inertia speed phase must still be undertaken tosynchronize the clutch required to be engaged for the destination fixedgear. In this instance, the oncoming clutch can be used to generateT_(C) as needed according to the methods described above. In theinstance of shifting to a mode state, a clutch is usually beingdisengaged, and the transmission operates on a remaining engaged clutch.However, in an EVT mode, a preferred input speed is utilized.Additionally, T_(O) must be maintained throughout the shift. A clutch,not to be actually engaged in the shift, can still be utilized toaccomplish a clutch assisted shift in a shift to mode. This clutch canbe partially actuated, generating slip and resulting T_(C) for useaccording to the methods described herein to affect T_(O). Once theshift is complete, this partially actuated clutch can be restored to anunlocked and desynchronized state.

FIG. 16 shows a control system architecture for controlling and managingtorque and power flow in a powertrain system having multiple torquegenerative devices, described hereinbelow with reference to the hybridpowertrain system shown in FIGS. 1 and 2, and residing in theaforementioned control modules in the form of executable algorithms andcalibrations. The control system architecture can be applied to anypowertrain system having multiple torque generative devices, including,e.g., a hybrid powertrain system having a single electric machine, ahybrid powertrain system having multiple electric machines, andnon-hybrid powertrain systems.

The control system architecture of FIG. 16 depicts a flow of pertinentsignals through the control modules. In operation, the operator inputsto the accelerator pedal 113 and the brake pedal 112 are monitored todetermine the operator torque request (‘T_(O) _(—) _(REQ)’). Operationof the engine 14 and the transmission 10 are monitored to determine theinput speed (‘N_(I)’) and the output speed (‘N_(O)’). A strategicoptimization control scheme (‘Strategic Control’) 310 determines apreferred input speed (‘N_(I) _(—) _(DES)’) and a preferred engine stateand transmission operating range state (‘Hybrid Range State Des’) basedupon the output speed and the operator torque request, and optimizedbased upon other operating parameters of the hybrid powertrain,including battery power limits and response limits of the engine 14, thetransmission 10, and the first and second electric machines 56 and 72.The strategic optimization control scheme 310 is preferably executed bythe HCP 5 during each 100 ms loop cycle and each 25 ms loop cycle.

The outputs of the strategic optimization control scheme 310 are used ina shift execution and engine start/stop control scheme (‘Shift Executionand Engine Start/Stop’) 320 to command changes in the transmissionoperation (‘Transmission Commands’) including changing the operatingrange state. This includes commanding execution of a change in theoperating range state if the preferred operating range state isdifferent from the present operating range state by commanding changesin application of one or more of the clutches C1 70, C2 62, C3 73, andC4 75 and other transmission commands. The present operating range state(‘Hybrid Range State Actual’) and an input speed profile (‘N_(I) _(—)_(PROF)’) can be determined. The input speed profile is an estimate ofan upcoming input speed and preferably comprises a scalar parametricvalue that is a targeted input speed for the forthcoming loop cycle. Theengine operating commands and the operator torque request are based uponthe input speed profile during a transition in the operating range stateof the transmission.

A tactical control scheme (‘Tactical Control and Operation’) 330 isrepeatedly executed during one of the control loop cycles to determineengine commands (‘Engine Commands’) for operating the engine, includinga preferred input torque from the engine 14 to the transmission 10 basedupon the output speed, the input speed, and the operator torque requestand the present operating range state for the transmission. The enginecommands also include engine states including one of an all-cylinderoperating state and a cylinder deactivation operating state wherein aportion of the engine cylinders are deactivated and unfueled, and enginestates including one of a fueled state and a fuel cutoff state.

A clutch torque (‘T_(CL)’) for each clutch is estimated in the TCM 17,including the presently applied clutches and the non-applied clutches,and a present engine input torque (‘T_(I)’) reacting with the inputmember 12 is determined in the ECM 23. A motor torque control scheme(‘Output and Motor Torque Determination’) 340 is executed to determinethe preferred output torque from the powertrain (‘T_(O) _(—) _(CMD)’),which includes motor torque commands (‘T_(A)’, ‘T_(B)’) for controllingthe first and second electric machines 56 and 72 in this embodiment. Thepreferred output torque is based upon the estimated clutch torque(s) foreach of the clutches, the present input torque from the engine 14, thepresent operating range state, the input speed, the operator torquerequest, and the input speed profile. The first and second electricmachines 56 and 72 are controlled through the TPIM 19 to meet thepreferred motor torque commands based upon the preferred output torque.The motor torque control scheme 340 includes algorithmic code which isregularly executed during the 6.25 ms and 12.5 ms loop cycles todetermine the preferred motor torque commands.

FIG. 17 is a schematic diagram exemplifying data flow through a shiftexecution, describing more detail exemplary execution of the controlsystem architecture such as the system of FIG. 16 in greater detail, inaccordance with the present disclosure. Powertrain control system 400 isillustrated comprising several hybrid drive components, including anengine 410, an electric machine 420, and clutch hydraulics 430. Controlmodules strategic control module 310, shift execution module 450, clutchcapacity control module 460, tactical control and operation module 330,output and motor torque determination module 340, and clutch controlmodule 490, are illustrated, processing information and issuing controlcommands to engine 410, electric machine 420, and clutch hydraulics 430.These control modules can be physically separate, can be groupedtogether in a number of different control devices, or can be entirelyperformed within a single physical control device. Module 310, astrategic control module, performs determinations regarding preferredpowertrain operating points and preferred operating range states asdescribed in FIG. 16. Module 450, a shift execution module, receivesinput from strategic control module 310 and other sources regardingshift initiation. Module 450 processes inputs regarding the reactivetorque currently applied to the clutch and the preferred operating rangestate to be transitioned to. Module 450 then employs programming,determining parameters for the execution of the shift, including hybridrange state parameters describing the balance of input torques requiredof the torque providing devices, details regarding a target input speedand input acceleration lead predicted required to execute the transitionto the preferred operating range state, an input acceleration leadimmediate as previously described, and clutch reactive torque leadimmediate min/max and clutch reactive torque immediate min/max values aspreviously described. From module 450, clutch reactive torque parametersand hybrid range state information are fed to clutch capacity controlmodule 460, lead control parameters and signals are fed to tacticalcontrol and operation module 330, and immediate control parameters andsignals are fed to output and motor torque determination module 340.Clutch capacity control module 460 processes reactive torque and hybridrange state information and generates logic describing clutch reactivetorque limits enabling engine control through module 330, electricmachine control through module 340, and clutch control through module490, in accordance with methods described herein. Tactical control andoperation module 330 includes means to issue torque requests and executelimits upon input torque supplied from engine 410, and feed,additionally, describe the input torque supplied from the engine tomodule 340 for use in control of electric machine 420. Output and motortorque determination module 340 likewise receives and processesinformation to issue electric machine torque requests to electricmachine 420. Additionally, module 340 generates clutch reactive torquecommands for use by clutch control module 490. Module 490 processesinformation from modules 460 and 340 and issues hydraulic commands inorder to achieve the required clutch torque capacity required to operatethe transmission. This particular embodiment of data flow illustratesone possible exemplary process by which a vehicular torque generativedevices and related clutches can be controlled in accordance with themethod disclosed herein. It will be appreciated by one having ordinaryskill in the art that the particular process employed can vary, and thisdisclosure is not intended to limited to the particular exemplaryembodiment described herein.

It is understood that modifications are allowable within the scope ofthe disclosure. The disclosure has been described with specificreference to the preferred embodiments and modifications thereto.Further modifications and alterations may occur to others upon readingand understanding the specification. It is intended to include all suchmodifications and alterations insofar as they come within the scope ofthe disclosure.

1. Method for controlling a powertrain comprising an electro-mechanicaltransmission mechanically-operatively coupled to an internal combustionengine and an electric machine adapted to selectively transmitmechanical power to an output member, the method comprising: monitoringa desired transmission shift; monitoring operational parameters of saidpowertrain; monitoring a maximum electric machine torque capacity;determining a desired output torque profile through said desiredtransmission shift; determining a maximum electric machine torquecapability profile through said desired transmission shift based uponsaid maximum electric machine torque capacity and said operationalparameters; comparing said desired output torque profile to said maximumelectric machine torque capability profile; determining a preferredoncoming clutch torque profile through said desired transmission shiftbased upon said comparing; and executing a clutch assisted shift basedupon said preferred oncoming clutch torque profile.
 2. The method ofclaim 1, further comprising monitoring a clutch power limit, whereindetermining said preferred oncoming clutch torque profile through saiddesired transmission shift is further based upon said clutch powerlimit.
 3. The method of claim 2, wherein determining said preferredoncoming clutch torque profile through said desired transmission shiftbased upon said clutch power limit comprises: determining a clutchenergy profile through said desired transmission shift by integrating aproduct of torque transmitted through an oncoming clutch and an oncomingclutch slip speed; comparing said clutch energy profile to said clutchpower limit through said desired transmission shift; and limiting saidoncoming clutch torque profile based upon said comparing said clutchenergy profile to said clutch power limit.
 4. The method of claim 1,wherein said powertrain further comprises a second electric machine,wherein monitoring said maximum electric machine torque capacitycomprises monitoring capabilities of said electric machines to providetorque together.
 5. The method of claim 1, wherein monitoringoperational parameters of said powertrain comprises: monitoring acurrent engine output; monitoring a current input speed of an inputmember to an oncoming clutch; monitoring a current output speed of anoutput member to said oncoming clutch; and monitoring a requested outputtorque.
 6. The method of claim 1, wherein executing said clutch assistedshift comprises: executing an clutch assisted portion of said desiredtransmission shift before an oncoming clutch achieves a slip speed equalto zero; and executing a synchronous portion of said desiredtransmission shift after said oncoming clutch achieves a slip speedequal to zero.
 7. The method of claim 1, wherein said desiredtransmission shift includes a shift to a mode operating range state, andwherein executing said clutch assisted shift based upon said preferredoncoming clutch torque profile comprises utilizing an oncoming clutch togenerate torque based upon said preferred oncoming clutch torque profileand then disengaging said oncoming clutch.
 8. Method for controlling apowertrain comprising an electro-mechanical transmissionmechanically-operatively coupled to an internal combustion engine and anelectric machine adapted to selectively transmit mechanical power to anoutput member, the method comprising: monitoring a desired transmissionshift; determining an oncoming clutch based upon said desiredtransmission shift; monitoring operation of said powertrain; determiningan output torque profile based upon said desired transmission shift andsaid operation of said powertrain; determining if said electric machinecan achieve said output torque profile; if said electric machine cannotachieve said output torque profile, determining if clutch assistedoperation of said oncoming clutch and said electric machine can achievesaid output torque profile; and if said clutch assisted operation ofsaid oncoming clutch and said electric machine can achieve said outputtorque profile, utilizing said clutch assisted operation of saidoncoming clutch and said electric machine to achieve said output torqueprofile.
 9. The method of claim 8, wherein determining said outputtorque profile is based upon transitioning an input member of saidoncoming clutch from an input speed synchronized to a current operatingrange state to a target input speed synchronized to a destinationoperating range state after a shift time.
 10. The method of claim 8,wherein determining if said electric machine can achieve said outputtorque profile comprises: determining a desired output torque profilebased upon said desired transmission shift and said operation of saidpowertrain; determining a maximum electric machine torque capacity basedupon said operation of said powertrain; determining a maximum electricmachine torque capability profile through said desired transmissionshift based upon said maximum electric machine torque capacity and saidoutput torque profile; and comparing said desired output torque profileto said maximum electric machine torque capability profile.
 11. Themethod of claim 10, wherein determining if said clutch assistedoperation of said oncoming clutch and said electric machine can achievesaid output torque profile comprises determining an output torquedeficiency profile through said desired transmission shift based uponsaid desired output torque profile and said maximum electric machinetorque capability profile
 12. The method of claim 8, further comprisingif said clutch assisted operation of said oncoming clutch and saidelectric machine cannot achieve said output torque profile, utilizingsaid engine, said clutch assisted operation of said oncoming clutch, andsaid electric machine to achieve said output torque profile.